Hi bluebug,
They’re the slatted type (see post #222 here).
You can read more about a solid surface base vs slats in post #10 here but if you already have a suitable base with a solid surface and you wanted to provide some extra ventilation under the mattress then something like the bed rug here or one of the slat conversions here (which has no flex at all) or even one of the Ikea slatted bed bases here (which has some flex which may change how the mattress feels and performs) could work well to increase ventilation for those who have a solid surface under their mattress and are lower cost options that would also be worth considering.
Phoenix